Bearing structure



Oct. 2, 1962 Filed Aug. 3, 1959 W. E. WOOLLENWEBER, JR., ETAL BEARINGSTRUCTURE 5 Sheets-Sheetl l fax/yep.

Oct. 2, 1962 w. E. wooLLENwEBER, JR., ETAL 3,056,634

BEARING STRUCTURE Filed Aug. 5. 1959 5 Sheets-Sheet 2 INVENToRs. JanisH. #f7/eax Oct. 2, 1962 w. E. WOOLLENWEBER, JR., ETAL 3,056,634

BEARNG STRUCTURE 5 Sheets-Sheet 3 Filed Aug. 5. 1959 IN VENTORS u c Ik.

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Oct. 2, 1962 w. E. wooLLENwEBER, JR., ETAL 3,055,634

BEARING STRUCTURE Filed Aug. 5, 1959 5 Sheets-Sheet 4 PIE. 8

50,000 REM. 60,000 REM.

70,000 REM. 78,000 R.P.M.

Oct. 2, 1962 W. E. WOOLLENWEBEIR, JR., ETAL BEARING STRUCTURE Filed Aug.3. 1959 5 Sheets-Sheet 5 50,000 REM.

70,000 R.P.M.

60,000 REM.

60,000 RPM.

IN VEN TORS. J'fmfs A. mamar. GERHARD PHI/L TKNEYS.

rates This invention relates generally to bearing structures and moreparticularly it relates to bearings especially adapted for use in highspeed machinery, such for example, as high speed air compressingdevices.

It is conventional to provide, in high speed machinery, anti frictionbearings and such bearings permit relatively high speed of shaftrotation. For example, speeds of the order of 60,000 `to 80,000revolutions per minute are attainable. However, such bearings havelimited life of Vthe order of 500 hours. Such limited life is tolerablein military aircraft applications where it is customary to repair orrebuild much of the mechanical equipment of the aircraft periodically,and after rather short periods of time. Such limited life is nottolerable in commercial applications.

High speed machinery, such as turbine driven air compressors forsupercharging internal combustion engines, has been adopted widely foruse on engines used for driving automobile trucks, tractors and asstationary power sources. For these applications of turbine drivencompressors the bearing structure must be adaptable to mass productionmethods and must be economical to manufacture. Also, such bearingstructure must have relatively long life and must not be subject tobreak down at relatively short intervals. Anti friction bearings forhigh speed machinery are excessively expensive and have too short anoperating life for application to turbine driven air compressors used oninternal combustion engines of the type previously described.

It is also conventional to provide sleeve bearings for high speedmachinery of all types including turbine driven air compressors.However, the speed of rotation of such machinery has been limitedbecause of the inability of sleeve bearings to tolerate a practicaldegree of unbalance in the rotating parts. Conventional sleeve bearingsare also objectionable in that they are incapable of damping resonantvibrations of the rotating parts at critical speeds.

It has been conventional practice to equip internal combustion engineswith air compressors for the purpose of increasing the power output ofthe engines by increasing the quantity of air fed to the combustionchamber of the engines. Rotational speeds of approximately 50,000revolutions per minute have been tolerable with convenventional sleevebearings, but there is a constant demand for more power output frompresent internal combustion engines and one way of accomplishing suchincrease of power output without redesigning the engine is by increasingthe rotational speed of the air input compressor. The phenomenon of oilfilm whir or shaft whipping has prevented increase of rotational speedsbecause this phenomenon in the journal bearings causes the shaft towhirl or whip instead of rotating about a stationary center. Thisphenomena is described in Mechanical Vibrations by Den Hartog, 2dedition, published in 1940 by McGraw-Hill Publishing Company, Inc. Theshaft whirlsV in such a manner that its center travels through acircular or modified circular path. Bearing clearances limit suchwhirling motion, but at speeds of the order of 80,000 revolutions perminute or more, it is found that the load on the bearing and thelubricating oil iilm dynamics are such that the oil film breaks down,thereby causing metal to metal contact and rapid wear of the bearings.

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When operating speeds of rotating machinery are increased beyond presentconventional levels, excessive oil iilm whirl may be prevented yto adegree by having relatively small clearances between the bearing and thejournal. With such clearance, the rotating shaft has little or nofreedom to move from the geometric center of the bearing. However, it isfound that conventional sleeve bearings are still not satisfactory whenclearances are so reduced.

Accordingly, the principal object of this invention is to provide abearing structure for high speed machinery of such nature that shaftwhirl is reduced to a minimum.

Another object of this invention is to provide a bearing structure whichwill permit substantial increase of normal operating speed of rotationof high speed machinery.

Still another object of this invention is to provide a bearing structurefor high speed machinery which will tolerate unbalance in the rotatingparts thereof.

Still another object of this invention is to provide a bearing structureinherently capable of providing relatively large damping effect andconsequent suppression of vibration of rotating parts.

A further object of this invention is to provide a bearing structure foraccomplishing the foregoing objects and of such nature that it may besubstituted for bearing structures of existing machinery withoutalteration of the component parts of such machinery.

In accordance with this invention there is provided a bearing structurefor high speed machinery comprising a bearing housing having at leastone journal box, a

bushing mounted within said journal box and having substantial clearancewith respect thereto, a shaft having a bearing surface disposed withinsaid bushing, said bushing having an internal diameter somewhat largerthan the `diameter of said shaft, means for inhibiting rota-tion of saidbushing with respect to said journal box, and a source of lubricantunder pressure for creating a film of lubricant between said bushing andsaid journal box and a iilm of lubricant between said b-ushing and saidshaft.

The full nature of the invention will be understood from theaccompanying drawings and the following description and claims:

FIG. 1 is a longitudinal cross-section of an air compressing deviceembodying the bearing structure of this invention.

FIG. 2 is a cross-section taken on line 2 2 of FIG. l.

FIG. 3 is an enlarged longitudinal cross-section of the bearing housingillustrated in FIG. l and illustrating a modilication of the sleevebearing of this invention.

FIG. 4 is an end view of the bearing sleeve illustrated in FIG. 3.

FIG. 5 is a cross-section taken on line 5--5 of FIG. 4.

FIG. 6 is a plan view of the thrust washer shown in FIG. 3 forpreventing rotation of the sleeve bearing.

FIG. 7 is a cross-section taken on line 7-7 of FIG. 6.

FIG. 8 is a graphical illustration of shaft motion in a conventionalbearing structure at speeds of 50,000 r.p.m., 60,000 r.p.m., 70,000r.p.m. and 78,000 r.p.m. respectively.

FIG. 9 is a graphical illustration of shaft motion in a bearingstructure embodying the invention., at the indicated speeds, andillustrating the stabilizing ability of this invention to suppress largeamplitude of whirl of the shaft center.

Referring to FIG. l of the drawings the invention isV radial inflowturbine wheel mounted on the common shaft 12 in conventional manner. Theturbine wheel 10 cooperates with a housing and nozzle ring generallyindicated at 14 having chambers designed in conventional manner so thatwheel 10 may provide power to drive the centrifugal air compressor wheel11, which in turn cooperates with a housing generally indicated at 15having chambers of such character that rotation of wheel 11 will providecompressed air.

In accordance with this invention, the shaft 12 includes a journalportion 17 which is supported for rotation within a bearing housing 18having journal boxes 19 and 20 for accommodating sleeve bearings orbushings 22 and 23 respectively. It is an important feature of thisinvention to provide substantial clearance between shaft 17 and theinternal surfaces of bushings 22 and 23, as at 24 (FIG. 2) and likewiseto provide substantial clearance between the internal surfaces ofjournal boxes 19 and and the external surfaces of bushings 22 and 23, asat 24a. This permits the bushings to float on films of lubricant withrespect to the shaft and the journal boxes.

The bushing 22 may be retained in the position shown in FIG. l by afirst thrust washer 25, a second thrust washer 26, a third thrust washer27, a rotatable thrust collar 28 and a wave spring 29, members 26, 27and 29 being clamped to the `bearing housing 19 by a capscrew 30 actingthrough the section 15a of outer housing 15. There is also provided athrust washer 32 against which is seated a coil spring 33. Coiled spring33 also seats on a thrust washer 34 thereby to exert pressure on theother bushing 23. Thrust washer 35 and snap ring 36 seated within agroove 37 in journal box 20 serve to retain all parts in properalignment within journal boxes 19 and 20.

For providing oil films between the bushings and the shaft andparticularly the bushings and the journal boxes, the bearing housing isformed to have an oil reservoir or chamber 40' into which oil may be fedunder pressure.

In operation, shaft 17 is driven by the radial inflow turbine 10 withthe exhaust gas from an internal combustion engine. The clearancebetween the bushings and the shaft and between the bushings and thejournal boxes permit oil or other lubricant to form films between theshaft and the bushings, and between the bushings and the journal boxes.Thus, the bushings tend to float between the oil films.

When the bushings float freely between the oil films it is found thatthere is excessive oil film whirl and shaft whip as illustrated by FIG.8. Tests have been made by means of electrical testing apparatus,including an oscilloscope. Each of the graphs in FIG. 8 represents thefluorescent screen of an oscilloscope on which is illustrated by thewhirling lines the trace formed on the fluorescent screen by theelectron beam. The trace of the electron beam represents the `shaft whipwhich occurs at speeds of 50,000 rpm., 60,000 rpm., 70,000 r.p.m., and78,000 rpm., in conventional turbine apparatus using bearings havingbushings which are free to float between the oil films. At 50,000 rpm.the degree of shaft whip is not excessive, but at 78,000 r.p.m. thephenomena of oil film whirl causes excessive shaft whip to the extentthat the oil films break down and cause rapid wear and destruction ofthe bearing.

The coil spring 33 functions to exert end-loading on the bushings 22 and23 in the form of pressure or restraining torque sufficient to preventthem from rotating to any substantial degree. As a result, the shaftrotates at relatively high speed with respect to the bushings, and thebushings rotate at relatively low speed with respect to the journalboxes. While the coil spring is illustrated and described herein as ameans of creating such end-loading and restraining torque, it isintended that any means for creating such end-loading and restrainingtorque shall be within the scope of this invention. For example, springforce, oil pressure or any other restraining means is adaptable to thisinvention so long as the restraining torque on the bushing is suflicientto reduce the speed of rotation of the bushing to such a value that oilfilm whirl does not develop on the outside of the bushing. It should befurther understood that it is within the scope of this invention toprovide restraining torque other than end-loading on the bushing. Forexample, such restraining torque may be applied to any portion of thebushing including the outer bearing surface thereof.

The structure described herein is found to permit speeds of rotationthat heretofore have been impossible without encountering destructivewhirling action of the shaft in conventional bearings or free floatingbushings. FIG. 9 of the drawings also represents the trace of anelectron beam on the screen of an oscilloscope by representing testsmade on the bearing of this invention. FIG. 9 shows that the applicationof end-loading or restraining torque by means of the coil spring 33reduces oil film whirl to such an extent that shaft whip is negligible.It will be noted that the trace of the cathode ray beam in FIG. 9 isgreatly reduced in amplitude as compared with FIG. 8. This reduction inamplitude provides clear indication that the degree of shaft whip atspeeds of from 50,000` r.p.m. to 80,000 rpm. is never sufficient tocause oil film whirl or to cause breakdown of the oil films. In otherwords, the movement of the shaft and the bushings never exceeds theclearances between the journal box, the bushings, and the shaft.

FIG. 3 of the drawings illustrates another modication of this inventionwherein there is provided a sleeve or bushing 42 mounted within thebearing housing 18 in journals 19 and 20. Sleeve 42 is a unitary elementmade of suitable bearing material and having clearance with respect tojournal boxes 19 and 20 as shown at 43 and 44. The shaft 17 also hasclearance with respect to the bushing 42 as indicated at 45 and 46. Aspreviously described in connection with FIG. l oil or other lubricantfrom chamber 40 creates a film within the clearance spaces 43, 44, 45and 46 so that the bushing floats between journal boxes 19 and 20 andshaft 17. It will be clear that the oil film within spaces 4S and 46 isprovided by a flow of oil from chamber 40 through the apertures 47 inbushing 42.

Referring to FIGS. 4, 5, 6 and 7, the bushing 42 is prevented fromrotating by slotting the left hand end of the `bushing to form aplurality of teeth 49. A thrust washer 50 is provided with slots 51 forreceiving the teeth 49 and is clamped in fixed relation to the journalbox 19 by means of the thrust washer 51a and outer housing section 15a,as previously described in connection with FIG. 1. Washers 50 and 51aare locked against rotation by means of a locking pin 53 extendingthrough the washers and into the journal box 19 as shown in FIG. 3. Theopposite end of bushing 42 bears on a flange 55 formed on shaft 17.Tests of this modification of the invention show results substantiallyidentical with or indistinguishable from the results shown in FIG. 9,and therefore, this figure of the drawings also illustrates that thismodification of the invention also prevents excessive oil film whirl andthe resulting damage to the bushing and bearing surfaces.

From the foregoing description, it will be apparent that this inventionprovides a bearing structure capable of tolerating high speeds ofrotation in various types of machines. FIGS. 8 and 9 of the drawingsclearly illustrate the increase of speed of rotation which is obtainablein accordance with this invention. It should be understood, however,that the upper limits of speed obtainable by the bearing structure ofthis invention are still unknown. This is because of the fact that ithas not been feasible to test turbine structures embodying thisinvention at speeds in excess of 80,000 r.p.m., because of the fact thatthe turbine wheel structure would not withstand higher speeds. Thephenomenon of oil film whirl is reduced to a negligible quantity wherebybreakdown of the film of lubricant is eliminated. Also, the necessityfor relatively small clearance is eliminated so that the effects ofcentrifugal force do not cause excessive. bearing loads. Furthermore,any slight unbalance in rotating parts is in effect neutralized by thespecial design of the bearing structure since the flexibility of thesystem allows the rotor to nd and rotate about its true center ofgravity.

This invention has the further advantage that it renders bearingstructures relatively insensitive to oil pressure, oil temperature andoil viscosity. Conventional bearing structures are very sensitive tothese factors insofar as oil film whirl is concerned. Experimental testsshow that the bearing structure of this invention prevents oil lm whirland shaft whip through wide ranges of oil pressure, oil temperature andoil viscosity,

The results described herein are accomplished in part by means of thefloating relationship of the bushing to the journal box and the shaft.This permits greater radial freedom of movement of the shaft because ofthe double oil film inside and outside of the bushing. The clearancesbetween the bushing and the shaft on the one hand and between thebushing and the journal box on the other hand can be kept small enoughto control oil lm whirl. However, such clearances provide sufficientradial freedom to tolerate a greater amount of unbalance in the.rotating parts than can be tolerated with a fixed bushing. Furthermorefloating bushings provide a relatively large degree of damping tosuppress vibration of the rotating parts. It is particularly to be notedthat this invention provides a means for preventing any substantialdegree of rotation of the bushing. Consequently, oil film whirl does notdevelop on the outside of the bushing and because of this, a wide rangeof clearance is possible between the outer surface of the bushing andthe journal box. The outer oil lm also helps to suppress any tendencyfor whirl to develop between the shaft and the bushing.

While this invention has been disclosed with particular reference tocentrifugal air compressors directly connected by a common shaft to aturbine, it will be readily understood that the invention is not to belimited to use in any specialized type of machinery, but is applicableto many different types of high speed machinery.

The invention claimed is:

1. A bearing structure for high speed machinery comprising a bearinghousing having spaced and aligned journal boxes, a shaft disposed withinsaid journal boxes, a pair of bushing -members mounted over said shaftin alignment with said journal boxes, said bushing members havingsubstantial clearance with respect to said shaft and said journal boxes,said bearing housing being formed to provide a chamber communicatingwith the clearance spaces between said bushings, said journal boxes andsaid shaft, said chamber providing a lubricant reservoir for supplying alm of lubricant within said clearance spaces, and a coil spring mountedover said shaft and bearing on the facing ends of said bushings forinhibiting rotation of said bushings with respect to said journal boxes.

2. A bearing structure for high speed machinery comprising a bearinghousing having spaced and aligned journal boxes, a shaft disposed Withinsaid journal boxes, a pair of bushing members mounted over said shaft inalignment with said journal boxes, said bushing members havingsubstantial clearance with respect to said shaft and said journal boxes,said bearing housing being formed to provide a chamber communicatingwith the clearance spaces between said bushings, said journal boxes andsaid shaft, said chamber providing a lubricant reservoir for supplying afilm of lubricant within said clearance spaces, and resilient meansbearing on the facing ends of said bushings for inhibiting rotation ofsaid bushings with respect to said journal boxes.

3. A bearing structure for high speed machinery comprising a bearinghousing having spaced and aligned journal boxes, a shaft disposed withinsaid journal boxes, a pair of bushing members mounted over said shaft inalignment with said journal boxes, said bushing members havingsubstantial clearance with respect to said shaft and said journal boxes,a source of lubricant under pressure cornmunicating with the clearancespaces between said bushings, said journal boxes and said shaft toprovide a film of lubricant within said clearance. spaces, and a coilspring mounted over said shaft and bearing on the facing ends of saidbushings for inhibiting rotation of said bushings with respect to saidjournal boxes.

4. A bearing structure for high speed machinery comprising a bearinghousing having a journal box, a shaft disposed within said journal box,a bushing member mounted over said shaft in lalignment with said journalbox, said bushing member having substantial clearance with respect tosaid shaft and said journal box, said housing being formed to provide alubricant chamber communicating with the clearance spaces between saidbushing, said journal box and said shaft, to provide a film of lubricantwithin said clearance spaces, and resilient means in said chamber andbearing on said bushing for inhibiting rotation of said bushing withrespect to said journal box.

5. A bearing structure for high speed machinery comprising a bearinghousing having a journal box, a shaft disposed Within said journal box,a bushing member mounted over said shaft in alignment with said journalbox, said bushing member having substantial clearance with respect tosaid shaft and said journal box, said housing being formed to provide alubricant chamber communicating With the clearance spaces between saidbushing, said journal box and said shaft, to provide a ilm of lubricantwithin said clearance spaces, and means in said chamber and engagingsaid bushing member endwise thereof at multiple points for inhibitingrotation of said bushing with respect to said journal box.

References Cited in the file of this patent UNITED STATES PATENTS1,020,423 Hewitt Mar. 19, 1912 2,532,795 Underwood et al Dec. 5, 19502,908,533 Schurr et al. Oct. 13, 1959

